Why was being a legionary in the army of the Late Roman Empire so unappealing to people considering their extreme salaries?

There are a few reasons why being in the legions were very unappealing, especially during periods when different reforms had come into effect meant to increase discipline among the soldiery. Recruits could be sent anywhere in the Roman Empire. It didn't matter where you were from, you could be stationed in extreme locations. For example, an Egyptian soldier who had to serve in Europe, and was subsequently forgotten by his family, despite his letters. If, like Polion, you were from Egypt and then were stationed in some place like Britania or Germania, the weather, culture, and language would be a significant shock. Getting from one part of the Empire to the other would have taken many months. Training could be brutal. After a number of reforms soldiers were required to carry all their own equipment and then some (some enterprising soldiers were known to have purchased mules to carry their equipment, which the military saw as opulent and lazy). Service was set around a minimum of 20 years after Augustus. The Roman legion operated almost exclusively in Latin, so soldiers not from Italy, or those who did not speak Latin were at a disadvantage.

These are just a few things. I’m being rushed out the door! Hope this helps!

As for the pay: it’s extremely difficult to properly translate their pay into modern terms. Under Septimius Severus pay was pegged to 500 denarii a year, but this didn’t mean they were paid that at the end of each year. Instead, they had their clothing, food, and other necessities docked from their pay, but how much this amounted to is unknown. Soldiers also relied on Emperor’s donations from time to time to supplement their income. Probably, much of their income came from booty acquired through war and pillaging (which was much more lucrative in the east than the west). However, if a soldier survived his entire period of service, he was rewarded with a one-time payment of a few thousand denarii or, in some cases, farmland that could vary widely in fertility. Another factor to keep in mind is during the 3rd and 4th century there were a series of devaluations of the coinage that dropped to such low levels that money became essentially worthless by the time Diocletian came to power in 284 AD, probably nullifying a goodly portion of a soldier’s wages. We could use Diocletian’s disastrous Price Edicts as way to gauge the worth of things, but this is difficult because they probably represent a maximum price tolerance, instead of their traditional value or their actual inflated value.

But do look up the Price Edicts for fun.